Design and Analysis of Truss Gen 2: EGB121 Engineering Mechanics

This report details the redesign process of 'Truss Gen 2', a steel truss intended to replace a failing component in an aggregate rock processing facility. The original truss failure was attributed to a single member exceeding its ultimate tensile strength. The redesigned truss, Truss Gen 2, was designed to withstand three times the original load, maintain the same dimensions, and be retrofitted to existing supports. The report covers the evaluation, modeling, and testing processes, including material properties, design methodology, and the final design. Key aspects include material selection (ASTM A992 Steel Alloy), a factor of safety of 2, increased cross-sectional area of members, and adjusted truss bay spacing. The report concludes with a statement of design compliance and references to supporting calculations and data.

Trusst Me Engineers
Truss Gen 2 Design Report
EGB121 Engineering Mechanics
Tut 6, Group 4 - Saeed Abdullah S Ain Aldeen (N9847301), Osama
Baqurayn ( N9644491), John Boyle, Nicholas Garai (N9949437), Archibald
Lightbody-Gee (N10138218)
4-26-2018

Contents
Executive Summary...............................................................................................................................2
1. Introduction...................................................................................................................................3
1.1 Context..................................................................................................................................3
1.2 Inclusions...............................................................................................................................3
2. Material Properties........................................................................................................................3
Fig 2.1 Stress-Strain Diagram.............................................................................................................3
Fig 2.2 Material Testing Result...........................................................................................................4
Fig 2.3 Deflection vs Load Graph.......................................................................................................4
Fig 2.4 Young’s Modulus Table..........................................................................................................4
2.1 Experimental Limitations.............................................................................................................5
2.2 Material Design Considerations.............................................................................................5
2.3 Materials Selection................................................................................................................6
3. Design Methodology......................................................................................................................6
3.2 Factor of Safety......................................................................................................................6
3.3 Material Specification............................................................................................................6
3.4 Cross-sectional Area of Members..........................................................................................6
3.5 Truss Bay Spacing...................................................................................................................6
3.6 Truss Member Layout............................................................................................................6
Fig 3.1 Table of Assumptions.............................................................................................................6
4. Final Design....................................................................................................................................7
Fig 4.1 Truss Gen 2.............................................................................................................................7
4.2 Statement of Design Compliance...........................................................................................7
5. Conclusions....................................................................................................................................7
6. References.....................................................................................................................................9
Appendices..........................................................................................................................................10
i. Truss Analysis Calculations......................................................................................................10
ii. Extended Material Data...........................................................................................................10
Sample Dimensions.........................................................................................................................10
iii. Extended table of assumptions................................................................................................10
iv. Meeting Minutes.....................................................................................................................11
v. Statement of Contributions.....................................................................................................17
i

Executive Summary
ARCHIE
Trusst me engineers firm was used by clients to come up with an advanced structure support for a
conveyor belts employed in most industries like the aggregate rock processing services failed at the
initial trial. This engineering research paper shows the process of evaluation, recommendation
solution as well as considerations for ten design. These are put forward by Trust me engineers for
the advanced truss (Truss Gen 2).
Immediately after finishing examination to the original truss, Trust Me Engineers determined the
mode of fiasco to be stable deflection created by a sole member surpassing the organization´s
crucial tensile strength. Lack of enough material properties were the chief reason of the preliminary
truss failure. For this reason a keen evaluation, testing and selection of the material was foundation
of design process of the Trusst Me Engineers for the Truss Gen 2 . Several non-destructive as well as
destructive tests were done in four different materials putting more focus on the yield stress as well
as ultimate tensile strength. The outcomes of these evaluation and tests of several materials against
six chief materials given.
Design Methodology
Final Design
Conclusions
ii

1. Introduction
This structural engineering report details the analysis and design process for ‘Truss Gen 2’, a steel
truss commissioned by the Client to replace a component of their aggregate rock processing facility
which failed during initial testing.
1.1 Context
Having completed an investigation into the mode of failure of the original truss (Truss Gen 1), Trusst
Me Engineers was commissioned by the Client to tender a design proposal for a redesigned truss.
Truss Gen 1 was found to have failed due to a single member exceeding its ultimate tensile strength
under load. The client has specified that Truss Gen 2 must be able to hold three times the original
aggregate rock load to allow for future expansion of their operations. In addition to this design
requirement, Truss Gen 2 must have the same dimensions as Truss Gen 1, and be able to be
retrofitted to the surrounding structure using existing supports.
1.2 Inclusions
This report will document the evaluation, modelling and testing processes which Trusst Me
Engineers undertook in designing Truss Gen 2. Various materials, internal member layouts and bay
spacings will be evaluated. All design decisions which are incorporated into the final truss will be
justified with the calculations and test results provided herein.
2. Material Properties
NICK
Single paragraph on the each experiment, ie what equipment was used, did you test to destruction
or not, how did the samples differ between lab 1 and 2
Fig 2.1 Stress-Strain Diagram
0 10 20 30 40 50 60 70
-100
0
100
200
300
400
500
600
700
Stainless Steel
MS Blackform
Al5052
Al5005
Strain (%)
Stress (MPa)
Stress-strain diagram from Lab 1
3

NICK
Add another graph zoomed in on the elastic section (with 0.2% proof yield stress)
Label the yield stress, the UTS and the fracture point
Fig 2.2 Material Testing Result
Material Stainless Steel MS Blackform Al5052 Al5005
Exp Pub Exp Pub Exp Pub Exp Pub
Young's
Modulus
357.42 193-200 455.90 203 [i] 208 70.3 [e] 241 69.5
Ultimate
Tensile
611 505 355 340-370 231 228 140 145-185
Yield Stress
(MPa)
242 215 308 250-370 175 193 120 110
Ductility % 65.0 70 34.0 31-41 11.5 12 7.4 -
Toughness
(kJ/m^3)
3417 - 1120 - 239 - 88 -
Modulus of
Resilience
365.5 - 109.8 - 58.2 - 154.2 -
Table of results from Lab 1 - various materials comparing experimental test results with published figures
Fig 2.3 Deflection vs Load Graph
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
0
0.5
1
1.5
2
2.5
3
Al (cant)
Al (simp)
Steel (cant)
Steel (simp)
Load (N)
Deflection (mm)
Deflection vs load graph from Lab 2 - aluminium and steel samples in both cantilever and simply supported
configurations
4

Fig 2.4 Young’s Modulus Table
Material Young's Modulus (GPa) Young's Modulus (Published) (GPa)
Steel (Cantilever) 153.1 193-200 [g]
Steel (Simply Supported) 181.2 193-200 [g]
Aluminium (Cantilever) 64.6 70.3 [e]
Aluminium (Simply Supported) 86.1 70.3 [e]
Table of results from Lab 2d
2.1 Experimental Limitations
The key limitation of the first practical, was that the method used to determine the young's modulus
of the materials was inaccurate, as an extensometer, or another more accurate method, was not
used to measure the elongation of the material.
Practical 2 was a far more accurate method of measuring the Young's Modulus of the material. This
is because measuring the deflection of a beam of the material [j] is more accurate than the method
used in the first practical; measuring the extension of the beam by the movement of the crossheads
[k].
Lab 2 tested beam deflection only within the elastic zone of each material. Because it tested
deflection in radians rather than stress in tension, far greater movement could be observed over a
much smaller load range. This resulted in a stress/strain curve that could be observed at a much
more useful scale, from which a more accurate Young’s modulus could be derived.
2.2 Material Design Considerations
In order to select the optimum material for Truss Gen 2, several key material properties must be
considered. As shown in the Feedback Report, Truss Gen 1 failed due to permanent deflection of
one member in tension. To prevent this, the revised truss must be constructed from a material with
a higher tensile yield stress. This means the material can handle more tensile load before it its
stress/strain graph changes from linear, elastic deformation to plastic deformation.
Young’s Modulus is the ratio of stress to strain in the elastic zone of a material’s stress/strain graph
[1]. In the context of material selection for this project, the chosen material must have a high
enough Young’s modulus that the truss won’t deflect so far under load as to cause significant
misalignment of the hopper or increase in tension of the conveyor belt which Truss Gen 2 must
support.
Ultimate Tensile Strength for deformable materials such as metal, is the load under which a material
will begin to experience a reduction in cross sectional area, or necking [2]. As necking should never
occur during general operation of the truss, this property comes into play when choosing a factor of
safety. For example, in the event the truss is overloaded by the chosen factor of safety, the UTS of
the material must be high enough to avoid catastrophic failure of the truss.
Ductility refers to how much tensile strain a material will undergo before rupturing [3] Selecting
more ductile materials for Truss Gen 2 is desirable as it means the structure can deform more before
catastrophic failure due to rupture. However, as noted above, care must be taken to ensure the
material still has a high enough yield strength to resist plastic deformation under normal design
loads.
5

Toughness is a materials ability to absorb energy without rupturing. It can be thought of as a
combination of strength and ductility [4]. The final choice of material for Truss Gen 2 must have
adequate toughness to withstand high dynamic loading due to aggregate rock shifting or falling onto
the conveyor belt. However calculation of dynamic loading is outside the scope of this report.
The final material property that was considered for this design is modulus of resilience. This is the
amount of energy per unit area that a material can absorb in the elastic zone of the stress/strain
graph [5]. In the context of truss design, modulus of resilience is a factor in determining how much
energy can be imparted into the structure by live loads before permanent deflection occurs.
2.3 Materials Selection
JOHN
ASTM A992 Steel Alloy
3. Design Methodology
3.2 Factor of Safety
In deciding the factor of safety for the truss, there are several things to consider. The first is that
many components in the final design will be under different types of stress. While this project only
considers axial loading on the truss members, this cannot be guaranteed in reality. Some key factors
that fall outside of the scope of our project, but should still be considered when selecting a factor of
safety for the design are potential corrosion, fatigue over time [b], and potential flaws in the
materials used, all of which reduce the actual load the truss may be able to carry. Another factor is
the potential for human error, or failure in a connected system, such as the conveyor, which may
result in loads higher than what the truss is designed for being applied. Designs are often built to
take between two to three times their intended loads [a], in order to ensure safety. Composite wood
member, steel plate trusses often use factors of safety between 2 and 3.5 [c]. Some legal safety
standards require trusses to use a factor of safety of at least 1.75 [a]. Common overall factors of
safety used in buildings are between 4 and 6, while bridges have factors of safety between 5 and 7
[d].
Due to these factors, and common industry practice, a factor of safety of 2 has been chosen for the
revised design, in order to ensure a reasonable standard of safety.
3.3 Material Specification
JOHN
Consider the cost of A992, and how easy it is to work with, is it easy to weld and cut? Corrosion
resistance? Are there any other practical considerations with using this material?
3.4 Cross-sectional Area of Members
OSAMA
We have chosen 3x the original cross sectional area, mention that this will increase self-weight,
this will also increase construction costs slightly as welding, cutting, lifting will be more difficult
6

3.5 Truss Bay Spacing
SAEED
We have gone down to 3 bays, this reduces self weight. The horizontal members are longer, but
as we assume all members are braced against buckling in compression, this is not a
consideration. Increasing length does not affect the strength of members in tension. (citation
re: axial loading being applied consistently throughout the member)
3.6 Truss Member Layout
OSAMA? NICK?
briefly consider the Howe, Pratt and Warren Truss (with verticals) truss designs. Make a judgment on
whether it will significantly affect the critical stresses.
Veronica said this afternoon that diagonals are zero force members, changing their direction doesn’t
affect the forces on the horizontal or vertical members as the structure is static.
Fig 3.1 Table of Assumptions
Table of the main assumptions made during the design of Truss Gen 2. These were made to either simplify the
truss analysis or in the absence of further information.
ASSUMPTION JUSTIFICATION LIMITATIONS OR EFFECTS
JOHN
Truss will not be subject to
excessive dynamic loads
The incorporation of dynamic
load factors into our truss
analysis is beyond the
expertise of Trusst Me
Engineers.
The final truss design will only
be certified to withstand the
static loads provided to us by
the client.
Truss will operate under
optimal environmental
conditions
We were not told the
temperature range in which
the truss would be operating,
therefore this is outside the
scope of material selection for
this design.
Material properties such as
Young’s Modulus, ductility and
Toughness can change
dramatically with ambient
temperature [1], [2], [3]
The self-weight of members
will apply forces on the joints
around.
Along with the forces being
applied to the truss and
certain joints and members
from the granite, conveyor
belt, etc., the weight of each
individual member is adding
extra force onto the joints
holding it.
By implementing this
assumption, we will find that
the net mass of the truss will
also be heavier resulting in
members needing to be
stronger to therefore make
truss able to hold itself up in
the certain positions it
required to be used at with no
deformation.
Consistency between
weights/size of all the
members will vary.
All beams that are being used
for the truss are all the exact
same size and weight with no
With the inconsistency of
dimensions, weight and other
specifications of the members
7

inconsistencies that could
come from the manufacturing
process.
used in the truss, this will
affect the truss and its
structural integrity as some
members might be made
thinner and smaller, making
them weaker in the end. Along
with this, in all calculations,
they have been considered to
be all even in dimensions and
weight
Forces are being applied
evenly to the two sides of the
truss.
The granite that falls onto the
conveyor belt is evenly spread
across the whole conveyor belt
creating even forces acting
down on the truss.
As there are two sides to the
truss and we are only
analysing one side, an
assumption has been made to
half all specifications that were
given. Therefore, when
calculations were made, they
have referred to the
assumption of the load is being
spread evenly on both sides of
the truss.
4. Final Design
ARCHIE
Concisely summarise the final design chosen, mention that the 2 zero force members at the end
were removed (check we can do this with veronica)
Fig 4.1 Truss Gen 2
ARCHIE
4.2 Statement of Design Compliance
SAEED
Explain or demonstrate that the design meets specification, including external loads, supports
reactions, internal forces and stresses
5. Conclusions
ARCHIE
Upon completing a detailed structural analysis, Trusst Me Engineers concludes that the truss failed
due to a particular member (denoted as AC in Fig. 3.1) exceeding its yield strength by 24.23 MPa.
This was caused by excessive tension in the member due to the combined self-weight of the truss and
external loads placed on it.
Assuming no loss of structural integrity due to damage, material or manufacturing defects, this report
concludes that this failure was due to error in the original design.
8

In the absence of design documentation for the truss, it is difficult to say how this error came about,
but Trusst Me Engineers speculates that the initial design may not have taken into account either self-
weight or irregularities in load distribution from the material being transported on the conveyor belt.
9

6. References
NICK
Feedback report references
[1] Egb121 Engineering Mechanics,
Mechanical and structural analysis for design work,
Queensland University of Technology, [Online Document] 2018, pp. 4
[2] R.C. Hibbler,
Statics and Mechanics of Materials, 4th edition. Pearson Australia, 2015, pp.
245
[3]
Report Writing and Presentation, Queensland University of Technology, [Online Document].
2018, pp. 1-3
Lab experiment published results References
[e] ASM Aerospace Specification Metals Inc.,
Aluminum 5052-H32, [Online Document]. Available:
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=ma5052h32 [Accessed May 20,
2018]
[f] aalco,
5005 - H34 Sheet, [Online Document]. Available:
http://www.aalco.co.uk/datasheets/Aluminium-Alloy-5005-H34-Sheet_137.ashx [Accessed May 20,
2018]
[g] ASM Aerospace Specification Metals Inc.,
AISI Type 304 Stainless Steel, [Online Document].
Available: http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=mq304a [Accessed May
20, 2018]
[h] Bluescope Steel, HA1S steel Datasheet, [Online Document]. Available:
http://steelproducts.bluescopesteel.com.au/download.cfm?downloadfile=B3A16AC9-6764-11D4-
989800508BA5461F&typename=bslLiterature&fieldname=filename [Accessed May 20, 2018]
[i] The Engineering Toolbox,
Young's Modulus of Elasticity for Metals and Alloys, [Online Document].
Available: https://www.engineeringtoolbox.com/young-modulus-d_773.html [Accessed May 20,
2018]
[j] QUT Science and Engineering Faculty (SEF), EGB121: Engineering Mechanics Laboratory 1:
Materials Properties Experiment, [Accessed May 23, 2018]
[k] QUT Science and Engineering Faculty (SEF), EGB121: Engineering Mechanics Laboratory 2 – Beam
Bending Experiment, [Accessed May 23, 2018]
10

Archies references
Young’s Modulus, University of Washington
https://depts.washington.edu/matseed/mse_resources/Webpage/Biomaterials/
young's_modulus.htmUltimate Tensile Strength, Corrosionpedia, 2018
https://www.corrosionpedia.com/definition/1126/ultimate-tensile-strength-uts
Ductility Explained: Tensile Stress and Metals, The Balance, TERENCE BELL October 08, 2017,
https://www.thebalance.com/ductility-metallurgy-4019295
Toughness, NDT Resource Centre, 2014
http://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/
Toughness.htm
Modulus of Resilience, EngArc, 2012
http://www.engineeringarchives.com/les_mom_modulusofresilience.html
Factor of safety section references
[a] Skaggs, T. D., Woeste, F. E., Dolan, J. D., & Loferski, J. R. 1994. Safety factors for metal-plate-
connected wood trusses: Theoretical design versus test specifications.
Forest Products
Journal, 44(9), 11. Available: https://gateway.library.qut.edu.au/login?url=https://search-proquest-
com.ezp01.library.qut.edu.au/docview/214632873?accountid=13380
[b] Hedaya, M., Elsabbagh, A., & Hussein, A. 2014.
Safety factor maximization for trusses subjected
to fatigue stresses. Engineering Optimization, 1–18. doi:10.1080/0305215X.2014.947974
[c] Structural Building Components Association, 2018.
Truss Design Factors Of Safety, [Online]
Available: https://www.sbcindustry.com/content/1/truss-design-factors-safety
[d] Engineering ToolBox, 2010.
Factors of Safety. [Online] Available:
https://www.engineeringtoolbox.com/factors-safety-fos-d_1624.html [Accessed May 2018]
Appendices
i. Truss Analysis Calculations
Include calcs for 3 and 5 bays as done by saeed and osama
11